JP2004244702A - Method of producing rare earth permanent magnet - Google Patents
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- JP2004244702A JP2004244702A JP2003037713A JP2003037713A JP2004244702A JP 2004244702 A JP2004244702 A JP 2004244702A JP 2003037713 A JP2003037713 A JP 2003037713A JP 2003037713 A JP2003037713 A JP 2003037713A JP 2004244702 A JP2004244702 A JP 2004244702A
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【０００１】
【発明の属する技術分野】
本発明は、Ｒ（ＲはＹを含む希土類元素の１種又は２種以上）、Ｔ（ＴはＦｅ又はＦｅ及びＣｏを主体とする少なくとも１種以上の遷移金属元素）及びＢ（ホウ素）を主成分とする磁気特性に優れた希土類永久磁石の製造方法に関するものである。
【０００２】
【従来の技術】
希土類磁石の中でもＲ−Ｔ−Ｂ系希土類永久磁石（以下、単に希土類永久磁石）は、磁気特性に優れていること、主成分であるＮｄが資源的に豊富で比較的安価であることから、需要は年々、増大している。従来、希土類永久磁石の磁気特性を向上させるため、種々の試みがなされている。その中でも磁石合金中の酸素濃度を低下させることは、高性能化のために有効である。しかし、磁石合金中の酸素濃度を低下させると焼結工程において結晶粒の粗大化や、局部的な異常粒成長が起こりやすくなる。このため焼結温度に対する組織変化が著しく、角形性の悪い磁石となりやすい。
そこで磁石合金の焼結工程での粒成長を抑制し、磁気特性と焼結温度幅を改善する方法が提案されている。例えば、特開２００２−７５７１７号公報では、Ｃｏ、Ａｌ、Ｃｕ、それにＺｒ、Ｎｂ又はＨｆを含有するＲ−Ｔ−Ｂ系希土類磁石合金の金属組織中に微細なＺｒＢ化合物、ＮｂＢ化合物又はＨｆＢ化合物（以下、Ｍ−Ｂ化合物ということがある）を均一に分散して析出させることにより、磁石合金の粒成長を抑制し、磁気特性と焼結温度幅を改善する報告がなされている。
【０００３】
【特許文献１】
特開２００２−７５７１７号公報（第１頁）
【０００４】
【発明が解決しようとする課題】
希土類永久磁石は、周知のように、粉末冶金法により製造される。この製造工程の概略を説明すると、所定組成の合金を得た後にこの合金を粉砕して粉末を作製し、所定の形状に成形した後に焼結するというものである。この製造工程において、粉砕を行う粉砕機、粉砕された粉末を搬送する搬送配管の内壁、あるいは成形体を得るために用いる成形機の金型の摩耗が大きいと、製造設備の寿命が短くなり、生産性を著しく低下させるという問題点を有する。したがって、粉砕機等の摩耗が少ないことが、工業的な生産においては極めて重要であり、特開２００２−７５７１７号公報に開示されたＭ−Ｂ化合物を焼結体中に分散させる方法においても、要求される事項である。
【０００５】
そこで本発明は、希土類永久磁石を製造する過程において粉砕機等の摩耗が抑制され、生産効率の高い希土類永久磁石の製造方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
かかる目的のもと、本発明者等は種々の形態を有する原料合金を用いてＭ−Ｂ化合物が焼結体中に分散された希土類永久磁石を製造した。その結果、ＭとＢの両者を含む原料合金を用いて希土類永久磁石を製造した場合に、粉砕機、搬送配管の内壁及び成形機金型の摩耗が著しく大きくなること、さらに、ＭとＢが共存しない原料合金を用いて希土類永久磁石を製造した場合には、粉砕機等の摩耗が著しく低減されることを知見した。
【０００７】
本発明は以上の知見に基づくものであり、Ｒ：２５〜３５ｗｔ％（ＲはＹを含む希土類元素の１種又は２種以上）、Ｂ：０．５〜４．５ｗｔ％、Ａｌ及びＣｕの１種又は２種：０．０２〜０．５ｗｔ％、Ｍ（ＭはＺｒ、Ｎｂ及びＨｆの１種又は２種以上）：０．０３〜０．２５ｗｔ％、Ｃｏ：４ｗｔ％以下（０を含まず）、残部実質的にＦｅからなる最終組成を有する焼結体からなるＲ−Ｆｅ−Ｂ系希土類永久磁石を製造する方法であって、この最終組成を構成する複数種の金属粉末からなる混合物を加圧成形して成形体を得る工程と、この成形体を焼結する工程とを備え、ＢとＭは、互いに異なる複数種の金属粉末に含まれることを特徴とする希土類永久磁石の製造方法である。
本発明によれば、ＭとＢが共存する原料合金を用いていないので、焼結工程以前に行われる粉砕工程、成形工程において、Ｚｒ、Ｎｂ又はＨｆとＢとを化合物の形態として存在させることなく処理できる。したがって、粉砕機及び成形機金型の摩耗が低減される。
なお、本発明において、金属粉末とは、単一種の金属元素（以下、単体金属という）粉末及び合金粉末を包含する概念を有している。したがって、金属粉末とは、合金粉末と合金粉末との組合せ、合金粉末と単体金属粉末との組合せの両者を包含することになる。
【０００８】
本発明において、Ｒ２Ｆｅ１４Ｂ化合物又はＲ２（Ｆｅ，Ｃｏ）１４Ｂ化合物を含む合金粉末（ａ）と、Ｍを含む金属粉末（ｂ）を複数種の金属粉末として含むことができる。ここで、合金粉末（ａ）は、Ｒ−Ｆｅ−Ｂ系希土類永久磁石の主相を構成するＲ２Ｆｅ１４Ｂ化合物又はＲ２（Ｆｅ，Ｃｏ）１４Ｂ化合物を含むが、これには２つの形態がある。１つは合金粉末（ａ）が専らＲ２Ｆｅ１４Ｂ化合物又はＲ２（Ｆｅ，Ｃｏ）１４Ｂ化合物からなるものであり、他の１つはＲ２Ｆｅ１４Ｂ化合物又はＲ２（Ｆｅ，Ｃｏ）１４Ｂ化合物のみならず所謂粒界相を構成する成分をも含むものである。前者の形態は、さらに、以下の２つの形態を含む。１つは、合金粉末（ａ）はＲ２Ｆｅ１４Ｂ化合物又はＲ２（Ｆｅ，Ｃｏ）１４Ｂ化合物が主体をなし、金属粉末（ｂ）はＲ及びＦｅを含み合金粉末（ａ）よりもＲ量が多い合金とする形態である。他の１つは、合金粉末（ａ）はＲ２Ｆｅ１４Ｂ化合物又はＲ２（Ｆｅ，Ｃｏ）１４Ｂ化合物が主体をなし、金属粉末（ｂ）はＭを構成元素とし、さらに、Ｒ及びＦｅを含み合金粉末（ａ）よりもＲ量が多い合金粉末（ｃ）が複数種の金属粉末の１つを構成する形態である。また、後者の形態としては、合金粉末（ａ）は実質的にＭを除いた前記最終組成を有し、金属粉末（ｂ）はＭを構成元素とするものである。
【０００９】
以上の本発明によれば、ＭとＢが共存しない原料を用いているため、焼結体中にＭ−Ｂ化合物が存在するＲ−Ｔ−Ｂ系希土類永久磁石を得ようとする場合に、Ｍ−Ｂ化合物は焼結工程中に生成されることになる。つまり本発明は、Ｒ２Ｔ１４Ｂ化合物相（ＲはＹを含む希土類元素の１種又は２種以上、ＴはＦｅ又はＦｅ及びＣｏを主体とする少なくとも１種以上の遷移金属元素）からなる主相と、主相よりＲを多く含む粒界相とを備えた焼結体からなり、ＺｒとＢとを含むＺｒＢ化合物、ＮｂとＢとを含むＮｂＢ化合物及びＨｆとＢとを含むＨｆＢ化合物の１種又は２種以上の化合物が分散する希土類永久磁石の製造方法であって、焼結工程中に前記化合物が生成することを特徴とする希土類永久磁石の製造方法を提供する。
【００１０】
以上の本発明において、焼結工程に供される成形体は、第１の粉末と第１の粉末とは異なる組成を有する第２の粉末との混合物から構成することができる。そして、この成形体において、Ｂを第１の粉末に含有させ、Ｚｒ、Ｎｂ及びＨｆの１種又は２種以上を第２の粉末に含有させることにより、焼結工程中に上記した化合物を生成させることができる。
【００１１】
【発明の実施の形態】
以下、本発明による希土類永久磁石の製造方法について詳細に説明する。
＜組織＞
はじめに本発明によって得られる希土類永久磁石の組織について説明する。
本発明によって得られる希土類永久磁石合金は、よく知られているように、Ｒ２Ｔ１４Ｂ化合物相（ＲはＹを含む希土類元素の１種又は２種以上、ＴはＦｅ又はＦｅ及びＣｏ）からなる主相と、この主相よりＲを多く含む粒界相とを少なくとも含んでいる。主相及び粒界相は、希土類永久磁石として通常含まれる相であるが、本発明では該合金の金属組織中に、ＺｒとＢとを含むＺｒＢ化合物、ＮｂとＢとを含むＮｂＢ化合物、及びＨｆとＢとを含むＨｆＢ化合物から選ばれる少なくとも１種の化合物を分散させることができる。
【００１２】
＜化学組成＞
次に、本発明による希土類永久磁石の望ましい化学組成について説明する。ここでいう化学組成は焼結後における最終組成をいう。
【００１３】
本発明の希土類永久磁石は、希土類元素（Ｒ）を２５〜３５ｗｔ％含有する。
ここで、Ｒは、Ｙを含む希土類元素（Ｌａ，Ｃｅ，Ｐｒ，Ｎｄ，Ｓｍ，Ｅｕ，Ｇｄ，Ｔｂ，Ｄｙ，Ｈｏ，Ｅｒ，Ｙｂ及びＬｕ）の１種又は２種以上である。希土類元素の量が２５ｗｔ％未満であると、希土類永久磁石の主相となるＲ２Ｔ１４Ｂ相の生成が十分ではなく軟磁性を持つα−Ｆｅなどが析出し、保磁力が著しく低下する。一方、希土類元素が３５ｗｔ％を超えると主相であるＲ２Ｔ１４Ｂ相の体積比率が低下し、残留磁束密度が低下する。また希土類元素が酸素と反応し、含有する酸素量が増え、これに伴い主に粒界相を構成する保磁力発生に有効なＲ−ｒｉｃｈ相が減少し、保磁力の低下を招く。そこで本発明では希土類元素の量を２５〜３５ｗｔ％とする。望ましい希土類元素の量は２８〜３３ｗｔ％、さらに望ましい希土類元素の量は２９〜３２ｗｔ％である。
Ｎｄは資源的に豊富で比較的安価であることから、希土類元素としての主成分をＮｄとすることが好ましい。
また、Ｄｙの含有はＲ２Ｔ１４Ｂ相の異方性磁界を増加させ、保磁力を向上させる上で有効である。よって、希土類元素としてＮｄ及びＤｙを選択し、Ｎｄ及びＤｙの合計を２５〜３３ｗｔ％とすることが望ましい。そして、この範囲において、Ｄｙの量は０．１〜８ｗｔ％が望ましい。Ｄｙは、残留磁束密度及び保磁力のいずれを重視するかによって上記範囲内においてその量を定めることが望ましい。つまり、高い残留磁束密度を得たい場合にはＤｙ量を０．１〜３．５ｗｔ％とし、高い保磁力を得たい場合にはＤｙ量を３．５〜８ｗｔ％とすることが望ましい。
【００１４】
また、本発明の希土類永久磁石は、ホウ素（Ｂ）を０．５〜４．５ｗｔ％含有する。Ｂが０．５ｗｔ％未満の場合には高い保磁力を得ることができない。ただし、Ｂが４．５ｗｔ％を超えると残留磁束密度が低下する傾向がある。したがって、上限を４．５ｗｔ％とする。望ましいＢの量は０．５〜１．５ｗｔ％、さらに望ましいＢの量は０．８〜１．２ｗｔ％である。
【００１５】
本発明による希土類永久磁石は、Ａｌ及びＣｕの１種又は２種を０．０２〜０．５ｗｔ％の範囲で含有することができる。この範囲でＡｌ及びＣｕの１種又は２種を含有させることにより、得られる希土類永久磁石の高保磁力化、高耐食性化、温度特性の改善が可能となる。Ａｌを添加する場合において、望ましいＡｌの量は０．０３〜０．３ｗｔ％、さらに望ましいＡｌの量は０．０５〜０．２５ｗｔ％である。また、Ｃｕを添加する場合において、望ましいＣｕの量は０．１５ｗｔ％以下（０を含まず）、さらに望ましいＣｕの量は０．０３〜０．０８ｗｔ％である。
【００１６】
本発明の希土類永久磁石は、Ｍ（ＭはＺｒ、Ｎｂ及びＨｆの１種又は２種以上）を０．０３〜０．２５ｗｔ％含有する。Ｍは希土類永久磁石の磁気特性向上を図るために酸素含有量を低減する際に、焼結過程での結晶粒の異常成長を抑制する効果を発揮し、焼結体の組織を均一かつ微細にする。したがって、Ｍは酸素量が低い場合にその効果が顕著になる。Ｍによる上記効果の発現理由は明らかではないが、本発明者は以下のように推測している。すなわち、焼結時に液相生成によって液相中のＢとＭが反応又は液相中へＭが含有されることによって液相の性質（濡れ等）が変化し、結果として焼結過程での異常粒成長が抑制される。この結果として、焼結後の粒界相（３重点に存在する相）中にＭを含む析出物（Ｍ−Ｂ化合物）が形成されるか、又はＭが固溶した粒界相が形成される。
Ｍの望ましい量は０．０５〜０．２ｗｔ％、さらに望ましい量は０．１〜０．１５ｗｔ％である。また、Ｍのなかでは、Ｚｒを選択することにより最も高い磁気特性を得ることができる。
【００１７】
本発明の希土類永久磁石は、その酸素量を２０００ｐｐｍ以下とすることが望ましい。酸素量が多いと非磁性成分である酸化物相が増大して、磁気特性を低下させるからである。そこで本発明では、焼結体中に含まれる酸素量を、２０００ｐｐｍ以下、望ましくは１５００ｐｐｍ以下、さらに望ましくは１０００ｐｐｍ以下とする。ただし、単純に酸素量を低下させたのでは、粒成長抑制効果を有していた酸化物相が減少し、焼結時に十分な密度上昇を得る過程で粒成長が容易に起こる。そこで、本発明ではＭを所定量添加する。
【００１８】
本発明の希土類永久磁石は、Ｃｏを４ｗｔ％以下（０を含まず）、望ましくは０．１〜１．０ｗｔ％、さらに望ましくは０．３〜０．７ｗｔ％含有する。ＣｏはＦｅと同様の相を形成するが、キュリー温度の向上、粒界相の耐食性向上に効果がある。
【００１９】
＜製造方法＞
次に、本発明による希土類永久磁石の製造方法について説明する。
原料合金中にＭとＢが共存しているとＭ−Ｂ化合物が形成されるが、本発明ではＭ−Ｂ化合物が存在する原料合金を用いないものとする。Ｍ−Ｂ化合物は融点が非常に高いため（例えばＺｒＢ２の融点は２９９０℃）、ＭとＢが共存する合金は、溶解・鋳造後の合金中に既にＭ−Ｂ化合物が生成していると考えられる。これらＭ−Ｂ化合物のビッカ−ス硬度は、Ｚｒ−Ｂ、Ｎｂ−Ｂ、Ｈｆ−Ｂ等で２０００Ｈｖ以上であり、主相を構成するＮｄ２Ｆｅ１４Ｂ化合物のビッカ−ス硬度（６００Ｈｖ）よりも著しく大きく、非常に硬い物質である。
Ｍ−Ｂ化合物を含むと著しく硬い当該化合物が粉末表面に露出することとなり、微粉砕装置の金属部材を削る作用が大きくなる、あるいは微粉砕工程後の成形工程での金型表面に与えるダメージが大きくなると解される。
そこで本発明は、原料合金中にＭとＢを共存させないことで、粉砕機等における摩耗劣化を軽減し、生産性を向上させるのである。
【００２０】
希土類永久磁石の製造方法としては、所望する組成と一致する単一の合金を出発原料とする方法（以下、単一法という）と、異なる組成を有する複数の合金を出発原料とする方法（以下、混合法という）の二つが存在する。本発明は、単一法及び混合法のいずれについても適用することができる。ここでは、混合法に本発明を適用する形態について説明する。
混合法は、Ｒ２Ｔ１４Ｂ化合物を主体とする合金（以下、低Ｒ合金ということがある）と、低Ｒ合金よりＲを多く含む合金（以下、高Ｒ合金ということがある）とを混合する。低Ｒ合金は本系磁石の主相を形成するためのものであり、高Ｒ合金は粒界相を形成するためのものである。低Ｒ合金にＣｏを含まない場合には低Ｒ合金はＲ２Ｆｅ１４Ｂ化合物を含む。また、低Ｒ合金にＣｏを含む場合にはＣｏがＦｅサイトに取り込まれるから、低Ｒ合金はＲ２（Ｆｅ，Ｃｏ）１４Ｂ化合物を含むことになる。
【００２１】
はじめに、原料金属を真空又は不活性ガス、好ましくはＡｒ雰囲気中で溶解し鋳造することにより、低Ｒ合金及び高Ｒ合金を得る。溶解、鋳造としては、アーク溶解、ストリップキャスト等の種々の手法を採用することができる。ここで、低Ｒ合金はＢを含むので、低Ｒ合金にはＭを含有させずに、高Ｒ合金にＭを含有させる。又は、低Ｒ合金及び高Ｒ合金のいずれにもＭを含有させることなく、低Ｒ合金及び高Ｒ合金のほかにＭを構成元素とする金属を用意する。
以上の金属（合金も含む）を得るための原料としては、希土類金属あるいは希土類合金、純鉄、フェロボロン、さらにはこれらの合金等を使用することができる。得られた鋳塊は、凝固偏析がある場合は必要に応じて溶体化処理を行なう。その条件は真空又はＡｒ雰囲気下、７００〜１５００℃の領域で１時間以上保持すれば良い。
【００２２】
以下では、高Ｒ合金にＭを含有させる形態について説明する。低Ｒ合金及び高Ｒ合金が作製された後、これらの各合金は別々に又は一緒に粉砕される。粉砕工程には、粗粉砕工程と微粉砕工程とがある。まず、各合金の鋳塊を、それぞれ粒径数１００μｍ程度になるまで粗粉砕する。粗粉砕は、スタンプミル、ジョークラッシャー、ブラウンミル等を用い、不活性ガス雰囲気中にて行なうことが望ましい。粗粉砕性を向上させるために、水素を吸蔵させた後、粗粉砕を行なうことも効果的である。
粗粉砕工程後、微粉砕工程に移る。微粉砕は、主にジェットミルが用いられ、粒径数１００μｍ程度の粗粉砕粉末が平均粒径３〜５μｍになるまで行われる。ジェットミルは、高圧の不活性ガス（例えば窒素ガス）を狭いノズルより開放して高速のガス流を発生させ、この高速のガス流により粗粉砕粉末を加速し、粗粉砕粉末同士の衝突やターゲットあるいは容器壁との衝突を発生させて粉砕する方法である。
本発明では、低Ｒ合金及び高Ｒ合金の各々にＭとＢが共存しないため、硬いＭ−Ｂ化合物が生成されていない。したがって、以上の粉砕工程、特に微粉砕に用いる粉砕機の磨耗を低減することができる。
【００２３】
微粉砕工程において低Ｒ合金及び高Ｒ合金を別々に粉砕した場合には、微粉砕された低Ｒ合金粉末及び高Ｒ合金粉末とを不活性ガス雰囲気中で混合する。低Ｒ合金粉末及び高Ｒ合金粉末の混合比率は、重量比で８０：２０〜９７：３程度とすればよい。低Ｒ合金及び高Ｒ合金を一緒に粉砕する場合の混合比率も同様である。微粉砕時に、ステアリン酸亜鉛等の添加剤を０．０１〜０．３ｗｔ％程度添加することにより、成形時に配向性の高い微粉を得ることができる。
【００２４】
次いで、低Ｒ合金粉末及び高Ｒ合金粉末からなる混合粉末を、電磁石に抱かれた金型内に充填し、磁場印加によってその結晶軸を配向させた状態で磁場中成形する。この磁場中成形は、１２〜１７ｋＯｅの磁場中で、０．７〜１．５ｔ／ｃｍ２前後の圧力で行なえばよい。
【００２５】
磁場中成形後、その成形体を真空又は不活性ガス雰囲気中で焼結する。焼結温度は、組成、粉砕方法、粒度と粒度分布の違い等、諸条件により調整する必要があるが、１０００〜１１００℃で１〜５時間程度保持すればよい。本発明は、この焼結工程においてＭ−Ｂ化合物が生成され、焼結体中に分散される。ただし、Ｍの全てがＢと化合物を形成するわけではなく、Ｂと化合物を形成しないこともある。
焼結後、得られた焼結体に時効処理を施すことができる。この工程は、保磁力を制御する重要な工程である。時効処理を２段に分けて行なう場合には、８００℃近傍、６００℃近傍での所定時間の保持が有効である。８００℃近傍での熱処理を焼結後に行なうと、保磁力が増大するため、混合法においては特に有効である。また、６００℃近傍の熱処理で保磁力が大きく増加するため、時効処理を１段で行なう場合には、６００℃近傍の時効処理を施すとよい。
【００２６】
以上では混合法に本発明を適用した形態のなかで高Ｒ合金にＭを含有せしめた例について説明した。この例をフローチャートにして示したのが図１である。図１において、高Ｒ合金と低Ｒ合金とを混合することにより、希土類永久磁石として所望される最終組成となる。なお、図１は低Ｒ合金及び高Ｒ合金を各々粗粉砕した後に混合し、しかる後に微粉砕する例を示したものであるが、微粉砕まで別個に行い、しかる後に低Ｒ合金と高Ｒ合金を混合することもできる。
【００２７】
前述したように、本発明は、低Ｒ合金及び高Ｒ合金のいずれにもＭを含有させることなく、かつ低Ｒ合金及び高Ｒ合金のほかにＭを構成元素とする金属を用意することができる。図２は、この形態をフローチャートとして示している。図２において、低Ｒ合金及び高Ｒ合金のほかにＭ金属／合金を作製する。ここで、「Ｍ金属／合金」とは、Ｍから選ばれる１種の元素（例えば、Ｚｒ）からなる純金属、Ｍから選ばれる２種以上の元素からなる合金（例えば、Ｚｒ−Ｎｂ合金、Ｚｒ−Ｈｆ合金）を含む。さらに、「Ｍ金属／合金」とは、Ｍから選ばれる１種又は２種以上の元素と他の金属元素との合金（例えば、Ｆｅ−Ｚｒ合金、Ｃｏ−Ｚｒ合金）とすることもできる。なお、混合の時期が粗粉砕後に限定されないことは、図１と同様である。
【００２８】
また、本発明が単一法に適用することができることは、前述の通りである。図３は単一法に本発明を適用した例をフローチャートとして示している。図３において、「主組成合金」とは、Ｍを除いて希土類永久磁石としての最終組成となる組成を有する合金を意味する。この主組成合金は、希土類永久磁石の主相をなすＲ２Ｔ１４Ｂ相を含み、かつ粒界相をも含んでいる。図３の例では、主組成合金を粗粉砕、微粉砕した後に、Ｍ金属／合金粉末を混合している。Ｍ金属／合金を粉末の状態として入手し、微粉砕された主組成合金粉末と混合することもできることを意味している。もちろん、主組成合金を粉末の状態で入手し、これまた粉末の状態として入手したＭ金属／合金と混合できることは言うまでもない。このとき、Ｍ金属／合金粉末は、主組成合金粉末よりも平均粒径が小さいことが望ましい。
【００２９】
【実施例】
次に、具体的な実施例を挙げて本発明をさらに詳細に説明する。
１）原料合金
ストリップキャスティング法により、表１に示す７種類の合金を作製した。なお、７種類の合金の中で、合金ａ−３及び合金ｂ−２はＭとＢが共存している。また、表１において、ＭはＺｒ、Ｎｂ及びＨｆのいずれかを示している。
【００３０】
【表１】
２）水素粉砕工程
表１に示す７種類の合金に対して室温にて水素を吸蔵させた後、Ａｒ雰囲気中で６００℃×１時間の脱水素を行なう水素粉砕処理を施した。
高磁気特性を得るために、本実験では焼結体酸素量を低く抑えるために、水素粉砕工程（粉砕処理後の回収）から焼結工程（焼結炉に投入する）までの各工程の雰囲気酸素濃度を１００ｐｐｍ未満に抑えてある。
【００３２】
３）混合工程
水素粉砕された各合金を表２の「合金組合せ」の欄に示す組合せによって「最終組成」となるように混合した。なお、混合に先立ってステアリン酸亜鉛を０．０５ｗｔ％添加し、ナウターミキサーで３０分間混合した。なお、表２において「Ｍ粉」とは、純度９９．９％、平均粒径３μｍのＺｒ粉末、Ｎｂ粉末及びＨｆ粉末のいずれかを示している。
【００３３】
【表２】
４）粉砕工程
通常、機械的手段による粗粉砕と微粉砕による２段粉砕を行なっているが、粗粉砕工程を１００ｐｐｍ未満の酸素濃度で行なうことができなかったため、本実施例では機械的手段による粗粉砕工程を省いている。
微粉砕はジェットミルを用いて行なった。得られた粉末の平均粒径は４μｍである。
【００３５】
５）成形工程
得られた微粉末を磁場中にて成形する。具体的には、微粉末を電磁石に抱かれた金型内に充填し、磁場印加によってその結晶軸を配向させた状態で加圧成形する。この磁場中成形は、１２〜１７ｋＯｅの磁場中で、０．７〜１．５ｔ／ｃｍ２前後の圧力で行なえばよい。本実験では１５ｋＯｅの磁場中で１．２ｔ／ｃｍ２の圧力で成形を行い、成形体を得た。
【００３６】
６）焼結、時効工程
得られた成形体を真空中において１０７０℃で４時間焼結した後、急冷した。焼結体の酸素濃度は、いずれも６００〜９００ｐｐｍであった。次いで、得られた焼結体に８００℃×１時間と５５０℃×２．５時間（ともにＡｒ雰囲気中）の２段時効処理を施した。
【００３７】
以上の粉砕工程に用いたジェットミルの摩耗状態の観察を行った。具体的には、ジェットミルの中でも最も摩耗が生じやすい配管の屈曲部について、以下の基準による観察を行った。結果を表３に示す。
○（粉砕機の摩耗が軽微）：５００ｋｇの原料を粉砕した際に粉砕機配管内の屈曲部の肉厚の摩耗が３％未満である。
×（粉砕機の摩耗が著しい）：５００ｋｇの原料を粉砕した際に粉砕機配管内の屈曲部の肉厚が３％以上減少している。
【００３８】
また、成形工程における金型の摩耗状態の観察も行った。具体的には、上述した条件（ただし、金型キャビティの寸法は１３×２２×１１ｍｍ）で３万ショットの連続成形を行った後に、以下の基準による観察を行った。結果を表３に示す。
○：３万ショット連続成形後、金型に摩耗なし
△：３万ショット連続成形はできたが、金型に摩耗あり
×：金型が欠け、３万ショットの連続成形ができない
【００３９】
さらに、時効処理後の永久磁石について、Ｂ−Ｈトレーサを用いて磁気特性を測定した。なお、各試料Ｎｏ．について２５個の永久磁石の磁気特性を測定し、その平均値を表３に示した。また、図４には、表２の試料Ｎｏ．１、５及び６による２５個の永久磁石の各保磁力（ＨｃＪ）をプロットした。なお、本発明による希土類永久磁石のいくつかについて組織を観察したところ、微細なＭ−Ｂ化合物の存在が確認された。
その一例として、試料Ｎｏ．１（本発明Ａ）のＥＰＭＡ（Ｅｌｅｃｔｒｏｎ Ｐｒｏｂｅ Ｍｉｃｒｏ Ａｎａｌｙｚｅｒ）による元素マッピングの結果を図５に、試料Ｎｏ．６（比較例Ｂ）のＥＰＭＡによる元素マッピングの結果を図６示す。なお、図５及び図６において、（ａ）はＢ（ホウ素）についてのマッピングを、（ｂ）はＺｒについてのマッピングを示している。図５及び図６において、丸で囲った領域ではＺｒとＢが同一の箇所に存在し、Ｚｒ−Ｂ化合物の存在が確認される。加えて、試料Ｎｏ．１では図５中で三角印で示す様に、ＺｒとＢが一致していない領域もあり、Ｚｒ−Ｂ化合物として存在しないＺｒに富む領域も確認された。
【００４０】
【表３】
表３に示すように、本発明Ａ〜Ｃは粉砕機の摩耗が軽微であったのに対して、比較例Ａ及びＢは粉砕機に著しい摩耗が生じた。また、本発明Ａ〜Ｃでは、成形後の金型を調べたところ、金型損傷や摩耗は見られず、成形体の寸法や外観に問題はなかった。比較例Ａでは金型損傷は見られないが、摩耗が多いために２．５万ショットで寸法及び外観の規格を外れる成形体が成形された。比較例Ｂでは成形体取出時に金型鳴きが発生した。さらに、１．８万ショットで成形体側面に欠けが生じ、２万ショットで金型が欠けたので、連続成形を終了した。また、比較例Ｃは、単一法でかつＭを含まないものであるが、その合金の組織を観察したところ、異常粒成長による粗大化した結晶粒子が多数確認された。その結果として、磁気特性、特に保磁力（ＨｃＪ）が劣っている。
【００４２】
以上の結果から、ＢとＭとが共存しない原料合金を用いると粉砕機及び金型の摩耗あるいは損傷が軽微であるのに対して、ＢとＭとが共存する合金（表１の合金ａ−３、合金ｂ−２）を用いると粉砕機及び金型の摩耗あるいは損傷が顕著となる。これは、前述したように、ＢとＭとが共存する合金には硬度の高いＭ−Ｂ化合物が析出しており、このＭ−Ｂ化合物が粉砕機及び金型の摩耗あるいは損傷を顕著にしているものと解される。なお、表３からわかるように、磁気特性の観点から、Ｍの中ではＺｒが最も有効である。
【００４３】
また、図４に示すように、本発明による希土類永久磁石は保磁力（ＨｃＪ）のばらつきが比較例による磁石に比べて小さい。したがって、本発明によれば、磁気特性が安定した永久磁石を得ることができるという効果をも有していることがわかった。その理由は明らかでないが、図５及び図６から考えるに、Ｚｒ−Ｂ（Ｍ−Ｂ）化合物として存在しないＺｒに富む領域の存在が保磁力（ＨｃＪ）のばらつき低減の一因であると推定される。
【００４４】
【発明の効果】
以上説明したように、本発明によれば、粉砕機等の摩耗が抑制され、生産効率の高い希土類永久磁石の製造方法が提供される。加えて本発明によれば、磁気特性、特に保磁力（ＨｃＪ）の安定した希土類永久磁石を製造することができる。
【図面の簡単な説明】
【図１】本発明の一形態を示す工程フローである。
【図２】本発明の他の形態を示す工程フローである。
【図３】本発明のさらに他の形態を示す工程フローである。
【図４】表３の試料Ｎｏ．１、５及び６による２５個の永久磁石の各保磁力（ＨｃＪ）をプロットしたグラフである。
【図５】表３の試料Ｎｏ．１のＥＰＭＡによる元素マッピングの結果を示す図である。
【図６】表３の試料Ｎｏ．６のＥＰＭＡによる元素マッピングの結果を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to R (R is one or more rare earth elements including Y), T (T is Fe or at least one transition metal element mainly composed of Fe and Co) and B (boron). The present invention relates to a method for producing a rare earth permanent magnet having excellent magnetic properties as a main component.
[0002]
[Prior art]
Among the rare earth magnets, RTB-based rare earth permanent magnets (hereinafter simply referred to as rare earth permanent magnets) have excellent magnetic properties and Nd as a main component is abundant in resources and relatively inexpensive. Demand is increasing year by year. Conventionally, various attempts have been made to improve the magnetic properties of rare earth permanent magnets. Among them, lowering the oxygen concentration in the magnet alloy is effective for improving the performance. However, when the oxygen concentration in the magnet alloy is reduced, the crystal grains become coarse and local abnormal grain growth easily occurs in the sintering step. For this reason, the structure changes remarkably with respect to the sintering temperature, and the magnet tends to have poor squareness.
Therefore, there has been proposed a method of suppressing grain growth in a sintering step of a magnet alloy and improving magnetic properties and a sintering temperature range. For example, in JP-A-2002-75717, a fine ZrB compound, NbB compound or HfB compound is contained in the metal structure of an RTB-based rare earth magnet alloy containing Co, Al, Cu, and Zr, Nb or Hf. It has been reported that by uniformly dispersing and precipitating (hereinafter, sometimes referred to as an MB compound), the grain growth of the magnet alloy is suppressed and the magnetic properties and the sintering temperature range are improved.
[0003]
[Patent Document 1]
JP-A-2002-75717 (page 1)
[0004]
[Problems to be solved by the invention]
As is well known, rare earth permanent magnets are manufactured by a powder metallurgy method. To explain the outline of the manufacturing process, after obtaining an alloy having a predetermined composition, the alloy is pulverized to produce a powder, formed into a predetermined shape, and then sintered. In this manufacturing process, if the crusher for crushing, the inner wall of the transfer pipe for transferring the crushed powder, or the mold of the forming machine used to obtain the formed body has a large wear, the life of the manufacturing equipment is shortened, There is a problem that productivity is significantly reduced. Therefore, it is extremely important that the wear of the crusher or the like is small in industrial production, and even in the method of dispersing the MB compound in a sintered body disclosed in JP-A-2002-75717, This is a required item.
[0005]
Accordingly, an object of the present invention is to provide a method of manufacturing a rare earth permanent magnet with high production efficiency, in which wear of a crusher or the like is suppressed in the process of manufacturing the rare earth permanent magnet.
[0006]
[Means for Solving the Problems]
With such a purpose, the present inventors have manufactured rare earth permanent magnets in which an MB compound is dispersed in a sintered body using raw material alloys having various forms. As a result, when a rare earth permanent magnet is manufactured using a raw material alloy containing both M and B, the wear of the pulverizer, the inner wall of the transfer pipe and the molding machine mold is significantly increased. It has been found that when a rare-earth permanent magnet is manufactured using a raw material alloy that does not coexist, wear of a crusher or the like is significantly reduced.
[0007]
The present invention is based on the above-described findings, and has a R content of 25 to 35 wt% (R is one or more of rare earth elements including Y), a B content of 0.5 to 4.5 wt%, and a content of Al and Cu. 1 or 2 types: 0.02 to 0.5 wt%, M (M is one or more of Zr, Nb and Hf): 0.03 to 0.25 wt%, Co: 4 wt% or less (0 Not included), the balance being a method for producing an R-Fe-B-based rare earth permanent magnet consisting of a sintered body having a final composition substantially composed of Fe, comprising a plurality of types of metal powders constituting the final composition. A step of obtaining a compact by press-molding the mixture; and a step of sintering the compact, wherein B and M are rare earth permanent magnets characterized by being contained in a plurality of different types of metal powders. It is a manufacturing method.
According to the present invention, since a raw material alloy in which M and B coexist is not used, Zr, Nb or Hf and B are present in the form of a compound in the pulverizing step and the forming step performed before the sintering step. Can be processed. Therefore, wear of the crusher and the mold of the molding machine is reduced.
In the present invention, the metal powder has a concept including a single kind of metal element (hereinafter referred to as a simple metal) powder and an alloy powder. Therefore, the metal powder includes both a combination of the alloy powder and the alloy powder and a combination of the alloy powder and the simple metal powder.
[0008]
In the present invention, R 2 Fe 14 B compound or R 2 (Fe, Co) 14 The alloy powder (a) containing the B compound and the metal powder (b) containing M can be included as a plurality of types of metal powders. Here, the alloy powder (a) is composed of R-Fe-B-based rare earth permanent magnets, 2 Fe 14 B compound or R 2 (Fe, Co) 14 Including the B compound, there are two forms. One is that alloy powder (a) is exclusively R 2 Fe 14 B compound or R 2 (Fe, Co) 14 B, and another one is R 2 Fe 14 B compound or R 2 (Fe, Co) 14 It contains not only the B compound but also a component constituting a so-called grain boundary phase. The former form further includes the following two forms. One is that the alloy powder (a) is R 2 Fe 14 B compound or R 2 (Fe, Co) 14 This is a form in which a B compound is a main component, and the metal powder (b) is an alloy containing R and Fe and having a larger amount of R than the alloy powder (a). Another one is that the alloy powder (a) is R 2 Fe 14 B compound or R 2 (Fe, Co) 14 The compound B is a main component, the metal powder (b) contains M as a constituent element, and the alloy powder (c) containing R and Fe and having a larger R content than the alloy powder (a) is one of a plurality of types of metal powder. This is a mode for configuring one. In the latter form, the alloy powder (a) has the final composition substantially excluding M, and the metal powder (b) contains M as a constituent element.
[0009]
According to the present invention described above, since a raw material in which M and B do not coexist is used, when an RTB-based rare earth permanent magnet in which an MB compound is present in a sintered body is to be obtained, The MB compound will be produced during the sintering process. That is, the present invention relates to R 2 T 14 A main phase composed of a B compound phase (R is one or more of rare earth elements including Y, and T is at least one transition metal element mainly composed of Fe or Fe and Co); One or more compounds of a ZrB compound containing Zr and B, an NbB compound containing Nb and B, and an HfB compound containing Hf and B, which are made of a sintered body having a grain boundary phase containing much. A method for producing a rare earth permanent magnet, wherein the compound is generated during a sintering step.
[0010]
In the present invention described above, the compact to be subjected to the sintering step can be composed of a mixture of the first powder and a second powder having a different composition from the first powder. Then, in this compact, B is contained in the first powder, and one or more of Zr, Nb and Hf are contained in the second powder, whereby the above-mentioned compound is produced during the sintering step. Can be done.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the method for producing a rare earth permanent magnet according to the present invention will be described in detail.
<Organization>
First, the structure of the rare earth permanent magnet obtained by the present invention will be described.
As is well known, the rare earth permanent magnet alloy obtained by the present invention has a R 2 T 14 It contains at least a main phase composed of a B compound phase (R is one or more rare earth elements including Y, T is Fe or Fe and Co), and a grain boundary phase containing more R than the main phase. . The main phase and the grain boundary phase are phases usually contained as a rare earth permanent magnet, but in the present invention, in the metal structure of the alloy, a ZrB compound containing Zr and B, an NbB compound containing Nb and B, and At least one compound selected from HfB compounds containing Hf and B can be dispersed.
[0012]
<Chemical composition>
Next, a desirable chemical composition of the rare earth permanent magnet according to the present invention will be described. The chemical composition here means the final composition after sintering.
[0013]
The rare earth permanent magnet of the present invention contains 25 to 35 wt% of a rare earth element (R).
Here, R is one or two or more of rare earth elements containing Y (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu). When the amount of the rare earth element is less than 25 wt%, R which is a main phase of the rare earth permanent magnet is 2 T 14 The formation of the B phase is not sufficient, and α-Fe or the like having soft magnetism is precipitated, and the coercive force is significantly reduced. On the other hand, if the rare earth element exceeds 35 wt%, the main phase of R 2 T 14 The volume ratio of the B phase decreases, and the residual magnetic flux density decreases. In addition, the rare earth element reacts with oxygen to increase the amount of oxygen contained therein. With this, the R-rich phase, which is mainly effective for generating the coercive force constituting the grain boundary phase, decreases, and the coercive force decreases. Therefore, in the present invention, the amount of the rare earth element is set to 25 to 35 wt%. A desirable amount of the rare earth element is 28 to 33 wt%, and a more desirable amount of the rare earth element is 29 to 32 wt%.
Since Nd is abundant in resources and relatively inexpensive, it is preferable that the main component as a rare earth element be Nd.
The content of Dy is R 2 T 14 This is effective in increasing the anisotropic magnetic field of the B phase and improving the coercive force. Therefore, it is desirable to select Nd and Dy as the rare earth elements, and to make the total of Nd and
[0014]
The rare earth permanent magnet of the present invention contains boron (B) in an amount of 0.5 to 4.5 wt%. If B is less than 0.5 wt%, a high coercive force cannot be obtained. However, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is set to 4.5 wt%. A desirable B amount is 0.5 to 1.5 wt%, and a more desirable B amount is 0.8 to 1.2 wt%.
[0015]
The rare earth permanent magnet according to the present invention may contain one or two of Al and Cu in a range of 0.02 to 0.5 wt%. By containing one or two of Al and Cu in this range, it is possible to increase the coercive force, increase the corrosion resistance, and improve the temperature characteristics of the obtained rare earth permanent magnet. When Al is added, a desirable amount of Al is 0.03 to 0.3 wt%, and a more desirable amount of Al is 0.05 to 0.25 wt%. In addition, when Cu is added, a desirable amount of Cu is 0.15 wt% or less (excluding 0), and a more desirable amount of Cu is 0.03 to 0.08 wt%.
[0016]
The rare earth permanent magnet of the present invention contains M (M is one or more of Zr, Nb and Hf) in an amount of 0.03 to 0.25 wt%. M has the effect of suppressing the abnormal growth of crystal grains during the sintering process when reducing the oxygen content in order to improve the magnetic properties of the rare earth permanent magnet, and makes the structure of the sintered body uniform and fine. I do. Therefore, the effect of M becomes remarkable when the oxygen amount is low. The reason why the above-mentioned effect is exhibited by M is not clear, but the present inventors presume as follows. In other words, during sintering, B and M in the liquid phase react with each other due to the formation of the liquid phase or M is contained in the liquid phase, thereby changing the properties (wetting, etc.) of the liquid phase, resulting in abnormalities in the sintering process. Grain growth is suppressed. As a result, a precipitate (MB compound) containing M is formed in the grain boundary phase (a phase existing at the triple point) after sintering, or a grain boundary phase in which M forms a solid solution is formed. You.
A desirable amount of M is 0.05 to 0.2 wt%, and a more desirable amount is 0.1 to 0.15 wt%. Also, among M, the highest magnetic characteristics can be obtained by selecting Zr.
[0017]
The rare earth permanent magnet of the present invention preferably has an oxygen content of 2000 ppm or less. This is because if the amount of oxygen is large, the oxide phase, which is a nonmagnetic component, increases, thereby deteriorating magnetic properties. Therefore, in the present invention, the amount of oxygen contained in the sintered body is set to 2000 ppm or less, preferably 1500 ppm or less, and more preferably 1000 ppm or less. However, if the amount of oxygen is simply reduced, the oxide phase having the effect of suppressing grain growth is reduced, and grain growth easily occurs in the process of obtaining a sufficient density increase during sintering. Therefore, in the present invention, a predetermined amount of M is added.
[0018]
The rare earth permanent magnet of the present invention contains Co in an amount of 4 wt% or less (excluding 0), preferably 0.1 to 1.0 wt%, and more preferably 0.3 to 0.7 wt%. Co forms a phase similar to that of Fe, but is effective for improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.
[0019]
<Production method>
Next, a method for manufacturing a rare earth permanent magnet according to the present invention will be described.
When M and B coexist in the raw material alloy, an MB compound is formed. However, in the present invention, a raw material alloy in which the MB compound is present is not used. The MB compound has a very high melting point (for example, ZrB 2 It is considered that the alloy in which M and B coexist has an MB compound already formed in the alloy after melting and casting. The Vickers hardness of these MB compounds is 2000 Hv or more in Zr-B, Nb-B, Hf-B, etc., and Nd constituting the main phase 2 Fe 14 It is a very hard substance that is significantly larger than the Vickers hardness (600 Hv) of the B compound.
When the MB compound is contained, the extremely hard compound is exposed on the powder surface, and the action of scraping the metal member of the pulverizing device is increased, or damage to the mold surface in the molding step after the pulverizing step is reduced. It is understood that it grows.
Therefore, the present invention reduces the wear deterioration in a pulverizer or the like and improves the productivity by preventing M and B from coexisting in the raw material alloy.
[0020]
Rare earth permanent magnets can be produced by a method using a single alloy having a desired composition as a starting material (hereinafter, referred to as a single method) or a method using a plurality of alloys having different compositions as starting materials (hereinafter, a single method). , The mixing method). The present invention can be applied to both the single method and the mixed method. Here, an embodiment in which the present invention is applied to the mixing method will be described.
The mixing method is R 2 T 14 An alloy mainly containing a B compound (hereinafter sometimes referred to as a low R alloy) and an alloy containing more R than the low R alloy (hereinafter sometimes referred to as a high R alloy) are mixed. The low R alloy is for forming a main phase of the present magnet, and the high R alloy is for forming a grain boundary phase. When the low R alloy does not contain Co, the low R alloy is R 2 Fe 14 B compound. Further, when Co is contained in the low R alloy, Co is taken into the Fe site, 2 (Fe, Co) 14 It will contain the B compound.
[0021]
First, a low R alloy and a high R alloy are obtained by melting and casting a raw material metal in a vacuum or an inert gas, preferably an Ar atmosphere. Various methods such as arc melting and strip casting can be employed for melting and casting. Here, since the low R alloy contains B, M is not contained in the low R alloy but M is contained in the high R alloy. Alternatively, a metal containing M as a constituent element is prepared in addition to the low R alloy and the high R alloy without containing M in any of the low R alloy and the high R alloy.
As a raw material for obtaining the above metals (including alloys), rare earth metals or rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. If there is solidification segregation, the obtained ingot is subjected to a solution treatment as necessary. The condition may be that the temperature is maintained at 700 to 1500 ° C. for one hour or more in a vacuum or Ar atmosphere.
[0022]
Hereinafter, an embodiment in which M is contained in the high R alloy will be described. After the low R and high R alloys have been made, each of these alloys is milled separately or together. The pulverizing step includes a coarse pulverizing step and a fine pulverizing step. First, the ingots of the respective alloys are coarsely pulverized to a particle size of about 100 μm. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill, or the like. In order to improve the coarse pulverizability, it is also effective to carry out coarse pulverization after absorbing hydrogen.
After the coarse grinding step, the process proceeds to the fine grinding step. The fine pulverization is mainly performed using a jet mill until the coarsely pulverized powder having a particle size of about 100 μm has an average particle size of 3 to 5 μm. A jet mill releases a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, accelerates the coarsely pulverized powder by the high-speed gas flow, and causes collision between the coarsely pulverized powders and a target. Alternatively, it is a method of crushing by generating collision with the container wall.
In the present invention, since M and B do not coexist in each of the low R alloy and the high R alloy, a hard MB compound is not generated. Therefore, abrasion of the pulverizer used for the above-mentioned pulverization step, particularly for fine pulverization, can be reduced.
[0023]
When the low R alloy and the high R alloy are separately pulverized in the pulverization step, the pulverized low R alloy powder and the high R alloy powder are mixed in an inert gas atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. The same applies to the mixing ratio when the low R alloy and the high R alloy are ground together. By adding an additive such as zinc stearate in an amount of about 0.01 to 0.3 wt% at the time of pulverization, a fine powder having high orientation at the time of molding can be obtained.
[0024]
Next, a mixed powder composed of a low R alloy powder and a high R alloy powder is filled in a mold held by an electromagnet, and is molded in a magnetic field with its crystal axis oriented by applying a magnetic field. This molding in a magnetic field is carried out in a magnetic field of 12 to 17 kOe and 0.7 to 1.5 t / cm. 2 What is necessary is just to carry out by pressure before and after.
[0025]
After compacting in a magnetic field, the compact is sintered in a vacuum or inert gas atmosphere. The sintering temperature needs to be adjusted according to various conditions such as the composition, the pulverizing method, and the difference between the particle size and the particle size distribution, but may be maintained at 1000 to 1100 ° C. for about 1 to 5 hours. In the present invention, an MB compound is generated in this sintering step and dispersed in the sintered body. However, not all of M forms a compound with B, and may not form a compound with B.
After sintering, the obtained sintered body can be subjected to an aging treatment. This step is an important step for controlling the coercive force. When the aging treatment is performed in two stages, it is effective to maintain the aging treatment at around 800 ° C. and around 600 ° C. for a predetermined time. When heat treatment at around 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. Further, since the coercive force is greatly increased by the heat treatment at around 600 ° C., when performing the aging treatment in one stage, it is preferable to perform the aging treatment at around 600 ° C.
[0026]
In the above, the example in which M is contained in the high R alloy in the form in which the present invention is applied to the mixing method has been described. FIG. 1 is a flowchart illustrating this example. In FIG. 1, the final composition desired as a rare earth permanent magnet is obtained by mixing a high R alloy and a low R alloy. FIG. 1 shows an example in which the low R alloy and the high R alloy are each coarsely pulverized and then mixed, and then finely pulverized. Alloys can also be mixed.
[0027]
As described above, according to the present invention, it is possible to prepare a metal containing M as a constituent element in addition to the low R alloy and the high R alloy without containing M in any of the low R alloy and the high R alloy. it can. FIG. 2 shows this form as a flowchart. In FIG. 2, an M metal / alloy is prepared in addition to the low R alloy and the high R alloy. Here, “M metal / alloy” means a pure metal composed of one element selected from M (for example, Zr), an alloy composed of two or more elements selected from M (for example, a Zr—Nb alloy, Zr-Hf alloy). Further, “M metal / alloy” may be an alloy of one or more elements selected from M and another metal element (for example, an Fe—Zr alloy, a Co—Zr alloy). Note that the timing of mixing is not limited after coarse pulverization, as in FIG.
[0028]
As described above, the present invention can be applied to a single method. FIG. 3 is a flowchart showing an example in which the present invention is applied to a single method. In FIG. 3, “main composition alloy” means an alloy having a composition that becomes a final composition as a rare earth permanent magnet except for M. This main composition alloy has a R phase which is a main phase of the rare earth permanent magnet. 2 T 14 It contains a B phase and also contains a grain boundary phase. In the example of FIG. 3, after the main composition alloy is roughly pulverized and finely pulverized, the M metal / alloy powder is mixed. This means that the M metal / alloy can be obtained in powder form and mixed with finely ground alloy powder of the main composition. Of course, it goes without saying that the main composition alloy can be obtained in powder form and mixed with the M metal / alloy obtained in powder form. At this time, it is desirable that the M metal / alloy powder has a smaller average particle size than the main composition alloy powder.
[0029]
【Example】
Next, the present invention will be described in more detail with reference to specific examples.
1) Raw material alloy
Seven kinds of alloys shown in Table 1 were produced by strip casting. In addition, M and B coexist in the alloy a-3 and the alloy b-2 among the seven types of alloys. Further, in Table 1, M represents any one of Zr, Nb and Hf.
[0030]
[Table 1]
2) Hydrogen grinding process
After hydrogen was absorbed at room temperature in the seven types of alloys shown in Table 1, a hydrogen pulverization treatment of dehydrogenation at 600 ° C. for 1 hour in an Ar atmosphere was performed.
In order to obtain high magnetic properties, in this experiment, in order to keep the amount of oxygen in the sintered body low, the atmosphere of each process from the hydrogen grinding process (recovery after the grinding process) to the sintering process (put into the sintering furnace) The oxygen concentration is kept below 100 ppm.
[0032]
3) Mixing process
Each of the alloys pulverized with hydrogen was mixed so as to have the “final composition” by the combination shown in the column of “alloy combination” in Table 2. Prior to mixing, 0.05% by weight of zinc stearate was added and mixed with a Nauta mixer for 30 minutes. In Table 2, “M powder” indicates any one of Zr powder, Nb powder, and Hf powder having a purity of 99.9% and an average particle diameter of 3 μm.
[0033]
[Table 2]
4) grinding process
Usually, two-stage pulverization by mechanical means of coarse pulverization and fine pulverization is performed. However, since the coarse pulverization step cannot be performed at an oxygen concentration of less than 100 ppm, in this embodiment, the coarse pulverization step by mechanical means is performed. Omitted.
Fine pulverization was performed using a jet mill. The average particle size of the obtained powder is 4 μm.
[0035]
5) Forming process
The obtained fine powder is molded in a magnetic field. Specifically, the fine powder is filled in a mold held by an electromagnet, and is subjected to pressure molding with its crystal axis oriented by applying a magnetic field. This molding in a magnetic field is carried out in a magnetic field of 12 to 17 kOe and 0.7 to 1.5 t / cm. 2 What is necessary is just to carry out by pressure before and after. In this experiment, 1.2 t / cm in a magnetic field of 15 kOe 2 The molding was performed under the pressure described above to obtain a molded body.
[0036]
6) Sintering and aging process
After sintering the obtained molded body at 1070 ° C. for 4 hours in a vacuum, it was rapidly cooled. The oxygen concentration of each of the sintered bodies was 600 to 900 ppm. Next, the obtained sintered body was subjected to two-stage aging at 800 ° C. × 1 hour and 550 ° C. × 2.5 hours (both in an Ar atmosphere).
[0037]
The wear state of the jet mill used in the above pulverization process was observed. Specifically, the following criteria were used to observe the bent portion of the pipe where the wear is most likely to occur in the jet mill. Table 3 shows the results.
（(Abrasion of the pulverizer is slight): When 500 kg of the raw material is pulverized, the abrasion of the thickness of the bent portion in the pulverizer pipe is less than 3%.
X (remarkable wear of the crusher): When 500 kg of the raw material was crushed, the thickness of the bent portion in the crusher pipe was reduced by 3% or more.
[0038]
Also, the state of wear of the mold in the molding process was observed. Specifically, 30,000 shots were continuously formed under the above-mentioned conditions (the dimensions of the mold cavity were 13 × 22 × 11 mm), and then observations were made according to the following criteria. Table 3 shows the results.
：: No mold wear after 30,000 shot continuous molding
Δ: 30,000 shots were continuously formed, but the mold was worn
×: The mold is missing, and 30,000 shots cannot be continuously formed.
[0039]
Furthermore, the magnetic characteristics of the permanent magnet after the aging treatment were measured using a BH tracer. In addition, each sample No. Were measured for the magnetic properties of 25 permanent magnets, and the average value is shown in Table 3. Further, FIG. The coercivity (HcJ) of each of the 25 permanent magnets according to 1, 5 and 6 was plotted. The structure of some of the rare earth permanent magnets according to the present invention was observed, and the presence of fine MB compounds was confirmed.
As an example, the sample No. FIG. 5 shows the results of element mapping of EPMA (Electron Probe Micro Analyzer) of Sample 1 (Invention A). FIG. 6 shows the result of element mapping of Comparative Example 6 (Comparative Example B) by EPMA. In FIGS. 5 and 6, (a) shows the mapping for B (boron), and (b) shows the mapping for Zr. In FIGS. 5 and 6, Zr and B are present at the same place in the circled region, and the presence of the Zr-B compound is confirmed. In addition, sample no. In FIG. 1, as indicated by triangles in FIG. 5, there were regions where Zr and B did not match, and regions rich in Zr that did not exist as a Zr-B compound were also confirmed.
[0040]
[Table 3]
As shown in Table 3, the crushers of the present inventions A to C showed slight wear, whereas the crushers of Comparative Examples A and B caused significant wear. In addition, in the present inventions A to C, when the mold after molding was examined, no damage or wear of the mold was observed, and there was no problem in the dimensions and appearance of the molded body. In Comparative Example A, although no damage to the mold was observed, a molded product out of the standard of dimensions and appearance was formed in 25,000 shots due to excessive wear. In Comparative Example B, mold squealing occurred during removal of the molded body. Further, chipping occurred on the side surface of the compact at 18,000 shots, and the mold was chipped at 20,000 shots. In Comparative Example C, which was a single method and did not contain M, when the structure of the alloy was observed, a large number of crystal grains coarsened due to abnormal grain growth were confirmed. As a result, the magnetic properties, especially the coercive force (HcJ), are inferior.
[0042]
From the above results, when a raw material alloy in which B and M do not coexist is used, the wear or damage of the pulverizer and the mold is slight, whereas an alloy in which B and M coexist (alloy a- 3. When the alloy b-2) is used, wear or damage of the pulverizer and the mold becomes remarkable. This is because, as described above, an MB compound having a high hardness is precipitated in an alloy in which B and M coexist, and this MB compound causes abrasion or damage of the pulverizer and the mold to be noticeable. It is understood that there is. As can be seen from Table 3, Zr is most effective among M from the viewpoint of magnetic properties.
[0043]
Further, as shown in FIG. 4, the rare-earth permanent magnet according to the present invention has a smaller variation in coercive force (HcJ) than the magnet according to the comparative example. Therefore, it has been found that the present invention has an effect that a permanent magnet having stable magnetic properties can be obtained. Although the reason is not clear, it is presumed from FIG. 5 and FIG. 6 that the existence of a Zr-rich region not present as a Zr-B (MB) compound contributes to a reduction in variation in coercive force (HcJ). Is done.
[0044]
【The invention's effect】
As described above, according to the present invention, a method for manufacturing a rare earth permanent magnet with high production efficiency, in which wear of a crusher or the like is suppressed is provided. In addition, according to the present invention, it is possible to manufacture a rare earth permanent magnet having stable magnetic properties, in particular, coercive force (HcJ).
[Brief description of the drawings]
FIG. 1 is a process flow illustrating one embodiment of the present invention.
FIG. 2 is a process flow showing another embodiment of the present invention.
FIG. 3 is a process flow showing still another embodiment of the present invention.
FIG. 4 shows sample Nos. It is the graph which plotted each coercive force (HcJ) of 25 permanent magnets according to 1, 5, and 6.
FIG. 5 shows sample Nos. FIG. 4 is a diagram showing the result of element mapping by EPMA of FIG.
FIG. 6 shows sample Nos. FIG. 6 is a view showing a result of element mapping by EPMA of No. 6;
Claims (7)
前記最終組成を構成する複数種の金属粉末からなる混合物を加圧成形して成形体を得る工程と、
前記成形体を焼結する工程とを備え、
ＢとＭは、互いに異なる前記複数種の金属粉末に含有されることを特徴とする希土類永久磁石の製造方法。R: 25 to 35 wt% (R is one or more of rare earth elements including Y), B: 0.5 to 4.5 wt%, and one or two of Al and Cu: 0.02 to 0.2. 5 wt%, M (M is one or more of Zr, Nb and Hf): 0.03 to 0.25 wt%, Co: 4 wt% or less (excluding 0), and the balance substantially consisting of Fe A method for producing an R-Fe-B-based rare earth permanent magnet comprising a sintered body having a composition,
Pressure molding a mixture of a plurality of types of metal powders constituting the final composition to obtain a molded body,
Sintering the molded body,
A method for manufacturing a rare earth permanent magnet, wherein B and M are contained in the plural kinds of metal powders different from each other.
前記主相よりＲを多く含む粒界相とを備えた焼結体からなり、
ＺｒとＢとを含むＺｒＢ化合物、ＮｂとＢとを含むＮｂＢ化合物及びＨｆとＢとを含むＨｆＢ化合物の１種又は２種以上の化合物が分散する希土類永久磁石の製造方法であって、
焼結工程中に前記化合物が生成することを特徴とする希土類永久磁石の製造方法。A main phase comprising an R 2 T 14 B compound phase (R is one or more of rare earth elements including Y, and T is at least one or more transition metal elements mainly composed of Fe or Fe and Co);
A sintered body having a grain boundary phase containing more R than the main phase,
A method for producing a rare earth permanent magnet in which one or more compounds of a ZrB compound containing Zr and B, an NbB compound containing Nb and B, and an HfB compound containing Hf and B are dispersed,
A method for producing a rare earth permanent magnet, wherein the compound is formed during a sintering step.
Ｂが前記第１の粉末に含有され、Ｚｒ、Ｎｂ及びＨｆの１種又は２種以上が前記第２の粉末に含有されることを特徴とする請求項６に記載の希土類永久磁石の製造方法。The compact to be subjected to the sintering step is composed of a mixture of a first powder and a second powder having a different composition from the first powder,
The method according to claim 6, wherein B is contained in the first powder, and one or more of Zr, Nb and Hf are contained in the second powder. .
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006265610A (en) * | 2005-03-23 | 2006-10-05 | Tdk Corp | Production method for rare earth sintered magnet |
| JP2006274304A (en) * | 2005-03-28 | 2006-10-12 | Tdk Corp | Method for producing r-t-b based sintered magnet |
| WO2010113371A1 (en) * | 2009-03-31 | 2010-10-07 | 昭和電工株式会社 | Alloy material for r-t-b-type rare-earth permanent magnet, process for production of r-t-b-type rare-earth permanent magnet, and motor |
-
2003
- 2003-02-17 JP JP2003037713A patent/JP4076080B2/en not_active Expired - Fee Related
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006265610A (en) * | 2005-03-23 | 2006-10-05 | Tdk Corp | Production method for rare earth sintered magnet |
| JP4556727B2 (en) * | 2005-03-23 | 2010-10-06 | Ｔｄｋ株式会社 | Manufacturing method of rare earth sintered magnet |
| JP2006274304A (en) * | 2005-03-28 | 2006-10-12 | Tdk Corp | Method for producing r-t-b based sintered magnet |
| JP4561432B2 (en) * | 2005-03-28 | 2010-10-13 | Ｔｄｋ株式会社 | Method for producing RTB-based sintered magnet |
| WO2010113371A1 (en) * | 2009-03-31 | 2010-10-07 | 昭和電工株式会社 | Alloy material for r-t-b-type rare-earth permanent magnet, process for production of r-t-b-type rare-earth permanent magnet, and motor |
| JP2011021269A (en) * | 2009-03-31 | 2011-02-03 | Showa Denko Kk | Alloy material for r-t-b-based rare-earth permanent magnet, method for manufacturing r-t-b-based rare-earth permanent magnet, and motor |
| CN102365142A (en) * | 2009-03-31 | 2012-02-29 | 昭和电工株式会社 | Alloy material for r-t-b-type rare-earth permanent magnet, process for production of r-t-b-type rare-earth permanent magnet, and motor |
| EP2415541A4 (en) * | 2009-03-31 | 2015-06-17 | Showa Denko Kk | Alloy material for r-t-b-type rare-earth permanent magnet, process for production of r-t-b-type rare-earth permanent magnet, and motor |
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